August 23, 2012

Dodecad Project components and East Eurasian-like admixture

I went back to the Dodecad Project K7b and K12b calculators, and calculated f4 statistics of the form:

f4(Southern_K7b, X, East_Asian_K7b, African_K7b)

I wanted to see how the various components related to East Eurasians.

Here are the results:

Visually for the West Eurasian components:

This shows the relative ordering of the different components on the East Asian-African axis. Notice that of the mainly Caucasoid components the most Asian-shifted is the North European component, the most African shifted is the Southwest Asian one. This makes sense because of the admixture phenomenon I've been describing in this series, and also the proximity of Arabia (which is where the Southwest Asian component is modal) to Africa.

The existence of East Eurasian-like admixture in Europe is further supported by the following observation: both the Atlantic_Baltic and North_European components (who are the most East Asian-shifted) are mainly geographically distributed to the west of the West Asian, Caucasus, and Gedrosia components (who are less East Asian-shifted). This seems discordant with geography. On the other hand, the relative position of the Caucasus, Southern, and Southwest Asian components vis a vis Africa are concordant with geography, as their center of distribution is close to Africa along land migration routes, with Southwest Asia being closer both genetically and geographically, and Caucasus most distant.

Another observation is that the Atlantic_Med component, which is modal in Sardinians and Basques is actually Asian-shifted relative to the Southern component (modal in Arabia).This might indicate the presence of some degree of East Eurasian-like admixture in Sardinia itself. So, while Sardinia may possess the minimum of this element in Europe, it may not do so in the wider Caucasoid world.

Unscrambling the omelette of West Eurasian origins is no easy task. Hopefully, new statistical methods and ancient DNA will help us achieve it.

8 comments:

We can see categories 'absorbing' East Asian admixture as we move through the K levels. I've always assumed that this is the reason Siberian admixture is reduced at higher K's: it's hiding in categories like Northern European. This is also true with SSA admixture, I've observed. 'North African' swallows up a lot of the African component at earlier K's, and presumably this is the cause of that component's relative shift toward sub-Saharan Africa. I've always interpeted this as being reflective of the age of the admxiture in question.

@pconroy it split on the euro7 calculator, but with an Fst of only 0.015. Given that the new ADMIXTURE 1.22 method for Fst's removes an upward bias, it's probably even a little lower than that.

So, splitting the North European component may be possible, but we're talking about very small differences. It's through the presence of other components (Med, West Asian, Siberian, etc.) that the northern European populations appear to differ from each other.

What's the possibility that some of this effect is caused by recent African-shifting in southern Europe as opposed to Asian-shifting in Northern Europe?

Since Europeans and Asians didn't separate for some 30/60ky after leaving Africa/Arabia, we would expect them to be much closer to each other genetically than to Africans. Even if there were no recent European/Asian admixture all Europeans would be "Asian-shifted" compared to Africans since they share a more recent command ancestor with Asians.

Following on from this, could not the apparent increase of Asian influence in the north/west be in part an increase of non-Asian admixture in the south/east? This might explain why the "Asian" influence appears to be related to distance from Africa not distance from Asia.

Interesting that the K12 Siberian component is "west" (positive end) shifted along this axis, relative to the K12 Southeast Asian and East Asian, when the K12 Southeast Asian, East Asian and Siberian components are roughly equidistant from the West Eurasian components (even the Northwest African), by FST distances - http://1.bp.blogspot.com/-kXZ8Mxu5dns/TybJ7CQJuPI/AAAAAAAAEbk/QYJc4rvQ3ww/s1600/fst.png.

Likewise for the East Asian component relative to the Southeast Asian component.

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